The field of art to which this invention pertains is catalysts and their supports.
Catalysts based on crystalline aluminosilicates which are prepared from a source of aluminum, a source of silicon, a source of alkali, a template (for example a tetrapropylammonium compound) and water, are known from U.S. Pat. No. 3,702,886. Depending on the composition of the starting mixture, the size of the primary crystallites is 1 micron or less. It was not realized that the size of the primary crystallites must not fall below a defined limit. Binders can be used for agglomerating primary crystallites, but no data are given on the size of the agglomerates and alumina is not mentioned as a binder. Neither are there any data on the particle size of the binder. If bentonite is used as the binder, the catalysts have an unfavorable pore distribution and a shorter life.
West German Patent No. DE 2,822,725 has disclosed the preparation of methanol conversion catalysts based on crystalline aluminosilicates. The diameter of the primary crystallites is 1 micron and greater. The object is the preparation of primary crystallites having diameters of much more than 1 micron. For this purpose, the crystal growth must be promoted by higher temperatures, and nucleation must be inhibited by low concentrations of the templates essential to the crystallization of the zeolites. Moreover, there are no references to the use of binders or to the size of the agglomerates.
According to West German Patent No. DE 2,405,909, the catalysts for hydrocarbon conversion are prepared on the basis of zeolites of the ZSM-5 type, the mean diameters of the primary crystallites being in the range from 0.05 to 0.1 micron. In this way, aging of the catalysts is to be delayed. The small primary crystallites, produced by setting a high stirrer speed, are difficult to filter off. Agglomerates of the order of size of 0.1 to 1 micron are produced from the primary crystallites. To prepare the catalysts, alumina as a binder is, inter alia, added to the agglomerates, other binders also being mentioned as equivalent. There are no data on the particle size of the agglomerates in the finished catalysts or of the binders. Moreover, the synthesis was carried out in the presence of sulfuric acid, using Al.sub.2 (SO.sub.4).sub.3 .multidot.xH.sub.2 O.
According to West German Patent No. DE-2,935,123, ZSM-5 or ZSM-11 zeolites are prepared with the use of ammonium hydroxide and an alcohol as the template, the presence of seeds being the distinctive feature. The zeolites are used as cracking and hydrocracking catalysts and also as catalysts for isomerization and dewaxing. Alumina can be used as a binder. There are no data, however, on the size of the primary crystallites or of the agglomerates and the binder.
A process for the preparation of zeolites and their use as catalysts for the conversion of aliphatic compounds into aromatic hydrocarbons is described in West German Patent No. DE-2,913,552. The template used is a mixture of butanol and ammonium hydroxide. The size of the primary crystallites is said to be less than 3 microns, preferably less than 2 microns. No lower limit is given. Alumina can, inter alia, be used as a binder for the agglomerates, but no particle sizes are given for the agglomerates and the binder.
West German Patent No. DE-3,537,459 has disclosed a process for the preparation of large, evenly shaped crystals of zeolites of the pentasil type from SiO.sub.2 and a compound of one or more trivalent elements, such as Al, B, Fe, Ga or Cr in amine-containing solutions, which comprises using fumed SiO.sub.2 produced by combustion of a silicon chloride as the SiO.sub.2 -containing starting material. The zeolites are used for the conversion of organic compounds, in particular for the conversion of methanol to hydrocarbons which contain lower olefins and aromatics. The zeolites obtained are not intergrown into agglomerates.
European Patent No. EP-173,901 relates to a process for the preparation of small zeolite crystallites of the ZSM-5 type having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of more than 5, corresponding to an Si/Al atomic ratio of more than 2.5. The smallest dimension of the crystallites is less than 0.3 micron. The crystallites are subjected to an ion exchange reaction and, after mixing with a matrix material, are molded into larger particles. These are dried and calcined, catalysts for various hydrocarbon conversion reactions being obtained. There are no data on the nature and the effect of the matrix material.
European Patent No. EP-123,449 describes a process for converting alcohol or ethers into olefins, using steam-treated zeolite catalysts; the latter have a crystal size of less than 1 micron and can be incorporated into a matrix. Clays, silica and/or metal oxides are mentioned as matrix materials.
U.S. Pat. No. 4,206,085 relates to hydrocarbon conversion catalysts based on zeolites and a matrix material, for increasing the abrasion resistance. The matrix material used is alumina from pseudoboehmite, and SiO.sub.2 from ammonium polysilicate or silica sol. The preferred zeolite is of the faujasite type. There are no data on the size of the zeolite crystals.